Development and application of a layered double hydroxides binding layer based DGT technique for simultaneous...

Simultaneous in-situ extraction is essential for elucidating the regulatory mechanisms of low molecular weight organic acids (LMWOAs) on arsenic (As) behaviors in soil. Building on validated sampling efficacy of As from soil and water, the diffusive gradients in thin-films (DGT) sampler with layered double hydroxide (LDHs) binding layer was developed in this work to extract tartaric, oxalic, fumaric, citric, and aconitic acid. The LDHs binding gel exhibited high adsorption capacities for LMWOAs (10.8-40.9 μmol/disc), with 96 %-112 % elution efficiency achieved within 60 min using an optimized mixed-acid eluent (50 mmol/L HCl-H₂SO₄). Performance of LDHs-DGT remained stable at pH 5-9 and ionic strengths ≤100 mmol/L (except fumaric acid). Spiking experiments with application of LDHs-DGT revealed that, citric acid enhanced As bioavailability in soil more effectively than other LMWOAs at equivalent concentrations. In addition, free citric acid (>2.1 mmol/kg, dry weight) in soil pore water was required to significantly enhance As bioavailability and mobility.